1. Field of the Invention
The present invention relates to a process and apparatus which in producing a sealed and packed bag, can process a bag for hand opening without reducing the mechanical strength of the bag until a user opens the bag. It relates more particularly to a process for processing an easy-opening and automatic bag-making packer employing an ordinary bag-making film and processing an easy-opening on the film when the film is fed from a roll of film.
2. Description of the Related Art
Conventionally, since a plastic bag made of polyethylene, polypropylene, polyester or nylon has advantages in that the bag can employ a film made thereof as a material for the bag, has good sealing performance, mechanical strength, printability and transparency and promotes efficiency by concurrently providing bag-making by heat seal and bag-packing, such a bag has been widely used in packing various products, e.g., liquid, powder, paste, solid or discrete products. However, long-term preservation of the contents in the bag has required use of a high-strength film, so that the bag must be cut and opened with a cutter.
Generally, the bag has a high mechanical strength but a low tear propagation strength, so that once the bag experiences an unintentional crack, a tear tends to easily propagate from the crack in an unintended direction. In order to improve the operability of a sealed bag, a heat sealed margin of the sealed bag has been provided with and I- or V-shaped notch extending toward the body of the bag. Thus, hand-pulling the heat sealed margin of the bag at the I- or V-shaped notch along the axis of the notch can provide an easy propagation of tear from the notch in an intended direction in the bag, even when made of plastic film of a high mechanical strength.
In addition, U.S. Pat. No. 4,543,279, for example, disclosed a prior art which provided a large number of microcuts which would not themselves reduce the mechanical strength of the bag and were arranged closely to one another along an edge of the heat sealed margin of a sealed bag. In detail, the opposite side margins of a blank film with a size and shape corresponding to those of a desired sealed bag first are provided with microcuts passing through each blank film, after which the blank film is rolled up on a hollow cylindrical roll core made of paper so that the microcuts in one side margin of the blank film will not overlap those in the other side margin of the blank film, and then the roll of film is mounted in an automatic bag-making packer. A means for providing the microcuts comprises a pair of pinch rollers feeding a blank film from a roll of film. One of the pinch rollers, a cutting roller, is made of a hard material and has a large number of edged projections. The other of the pinch rollers, a receiving roller, is made of a material, e.g. rubber, of a surface hardness providing a hardness supporting the cutting roller to form the microcuts in the blank film and also a softness protecting the edged projections from quick wear. Since the edged projections of the cutting roller pass through each side margin of the blank film to penetrate the receiving roller, the receiving roller is quickly worn without a surface cover thereon. Actually, in order to minimize this wear in the receiving roller, a gummed plastic-sheet tape has been attached around the receiving roller. The position of attachment of the tape must be changed two or three times a day during operation of the microcuts-providing means, or the tape must be exchanged in order to reduce wear in the receiving roller.
Thus, the first and second prior-art processes described above require high accurate positioning of a notch or microcuts in the blank film in order to produce a complete sealed and packed bag. In addition, apparatuses for the first and second prior-art processes also require a high accurate positioning of the notch or microcuts.
Thus, an automatic bag-making packer including a microcut former or notch former will produce a sealed and packed bag with an easy-opening processing from an ordinary plastic film.
The present inventors have studied such a machine from various viewpoints. A roll of film mounted in an automatic bag-making packer cannot be free from transverse rocking in feeding the film. Transverse rocking of the roll of film will constitute no problem on an automatic bag-making packer without a microcut or notch former but will fail to provide adequate accuracy in positioning microcuts or a notch by means of an automatic bag-making packer with a microcut or notch former providing microcuts or a notch or film which has been dispensed from the roll of film. In addition, since reducing the size of an automatic bag-making packer has been generally promoted and the automatic bag-making packer has been designed to operate adequately in as small a space as possible, securing a space in the automatic bag-making packer for stably receiving pinch rollers comprising a cutting roller and a mating or receiving roller is difficult. Even if the automatic bag-making packer can secure this space, the packer must increase in size and be more complicated in structure.